Spinal surgery often requires different appliances to be attached to the spine in order to achieve a certain surgical goal. For example, in the area of spinal fusion, the spinal disc is removed between adjacent vertebrae and an appliance is attached which distracts and compresses adjacent vertebrae together. The resulting bone-on-bone contact of adjacent vertebrae results in the vertebrae fusing together, provided that the adjacent vertebrae are held in relative stationary contact over time. A variety of appliances have been devised which attach to the spinal vertebrae to keep them stationary so that fusion can occur.
One type of appliance relates to a system of pedicle screws comprising screws having head segments wherein fusion rods are inserted into the head segments. Exemplary of this type of system are those manufactured by Medtronic, Inc., Synthes Inc., and Depuy Inc. A number of pedicle screws are installed on the spine, appropriate to the number of vertebrae desiring to be fused. The head segments pivot on the screw portion and are aligned so that their open sides are parallel with the vertical axis of the spine and a fusion rod of appropriate length is placed in the heads of adjacent pedicle screws, the rod subsequently being locked down inside the head segment with lock nuts.
The use of pedicle screws to anchor a spinal appliance works well with healthy, young bone; however where the bone has become osteoporotic, as in the case with older patients, the screws often become loose or back out. One solution to this problem has been to attach the fusion rods to the spine using nylon sub-laminar straps. This procedure is described in O'Brien et al., “Nylon Sublaminar Straps in Segmental Instrumentation for Spinal Disorders,” Clinical Orthopedics and Related Research, Number 203 February 1986 pg. 168. The nylon sub-laminar straps are non-invasive, and can be wrapped around the vertebrae. However, these sub-laminar straps do not attach the fusion rods in a locked-down fashion, and therefore, do not lock the vertebrae in a sufficiently stationary manner. Therefore, the vertebrae cannot be sufficiently distracted and compressed together for proper fusion using these types of sub-laminar straps.
United States Patent Application No. 20090105761 (Robie) represents a system for anchoring adjacent spinal vertebrae without using a screw system. This invention uses a type of strap that is anchored by staples to an inferior vertebral body wherein the strap is further threaded through the spinous process of the superior vertebral body thus tying together two adjacent vertebrae. This patent application does not address the issue of its performance in osteoporotic bone. The dependence of this system on staples may be a drawback, as stapling to a foundation of osteoporotic bone may not result in a long-term anchoring of the strap if the staple eventually works free.
The foregoing reflects the state of the art of which the inventor is aware, and is tendered with a view toward discharging the inventor's acknowledged duty of candor, which may be pertinent to the patentability of the present invention. It is respectfully stipulated, however, that the foregoing discussion does not teach or render obvious, singly or when considered in combination, the inventor's claimed invention.